1. Field of the Invention
Aspects of the present invention relate to a membrane-electrode assembly for a fuel cell, a method of manufacturing the same, and a fuel cell system including the same. More particularly, aspects of the present invention relate to a membrane-electrode assembly for a fuel cell that can implement fuel supply and release of a reaction product, and increase catalyst activity, and thereby can improve power characteristics of a fuel cell, a method of manufacturing the same, and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system to produce electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell, which uses methanol as a fuel.
The polymer electrolyte fuel cell is advantageous as the PEMFC provides a high energy density, but the PEMFC requires the need to carefully handle hydrogen gas and requires accessory facilities, such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like to produce hydrogen for the fuel gas.
On the contrary, the direct oxidation fuel cell has a lower energy density than that of the PEMFC, but the DOFC requires fuel that is easy to handle, is capable of operating at room temperature due to its low operation temperature, and does not need additional fuel reforming processors.
In the above-described fuel cells, the fuel cell stack that generates electricity substantially includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane disposed between them. The MEAs are disposed between adjacent bipolar plates to form the fuel cell stack.
A fuel is supplied to the anode and absorbed in a catalyst thereof, and the fuel is oxidized to produce protons and electrons. The electrons are transferred to the cathode via an external circuit, and the protons are transferred to the cathode through a polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted using a catalyst at the cathode to produce water. As the electrons flow from the anode to the cathode through the external circuit, the electrons produce useable electricity.